The present invention relates to a new structure of a static induction thyristor (hereafter referred to as an "SI thyristor"). Particularly, the invention relates to a structure of an insulated gate-controlled (MOS-Controlled) SI thyristor in which a gate drive circuit can be simplified.
An SI thyristor is a switching device of latching-up type, and driving of the SI thyristor has conventionally been executed by applying a positive trigger bias and a negative quench bias onto a gate. An example of the conventional driving circuit of an SI thyristor is illustrated in FIGS. 1a of the attached drawings.
In FIG. 1a, the junction gate SI thyristor is operated by respectively inputting of a trigger pulse .PHI..sub.ON and a quench pulse .PHI..sub.OFF into a buffer circuit having a P-channel MOS transistor 52 and a positive bias power source 54, and an N-channel MOS transistor 53 and a negative bias power source 55. The trigger pulse .PHI..sub.ON and the quench pulse .PHI..sub.OFF are respectively inputted at timing illustrated in FIG. 1b. Further, a resistor 57 is inserted between the buffer circuit and a gate of the SI thyristor unit 51, for limiting the current flowing into the gate of the SI thyristor unit 51. A capacitor 56 is a speed-up condenser. A diode 58 is provided so that the current from the gate at turn-off is not limited by the resistor 57. In this approach, conventional problems include that a control circuit for generating the trigger pulses and the quench pulses are complicated in structure, and that there are many parts for the buffer. In order to solve these problems, a driving method illustrated in FIGS. 2a and 2b has been proposed in Japanese Patent Application No. SHO 63-108572 entitled "A driving method of a static induction thyristor".
In FIG. 2a, the reference numeral 1 denotes a junction gate SI thyristor unit of the normally-off type. The SI thyristor unit has a pn junction gate to which a capacitor 2 is connected. A P-channel MOS transistor 31 is connected to a location between the gate and a cathode of the SI thyristor 1. The MOS transistor 31 has a gate which is controlled by pulse .PHI..sub.G which serve as input pulse to the capacitor 2. A waveform of the pulse .PHI..sub.G is illustrated in FIG. 2b.
As shown in FIG. 2b, the pulses .PHI..sub.G have an electric potential of V.sub.off at a period of time T.sub.1. By this potential, the MOS transistor 31 is brought to an "on" state or a conductive state under which there is the same potential at the gate and the cathode of the SI thyristor unit 1 so that the SI thyristor unit 1 is under a block state. When the potential of the pulse .PHI..sub.G is changed from V.sub.off to V.sub.on at time t.sub.1, the potential barrier in the channel of the SI thyristor unit 1 is reduced by capacitive coupling. At this time, the MOS transistor 31 is brought to the cut-off state.
The SI thyristor unit of normally-"off" type shifts from the blocking state to the "on" state, if slight voltage is given which corresponds to a diffusion potential between the gate and the cathode. At this time, the gate current is not required except for a part required to charge the input capacitance necessary for the gate to operate, and it is not required to cause direct current to flow.
At a period of time T.sub.2, the SI thyristor unit 1 is brought to an "on" state.
When the pulses .PHI..sub.G are changed from V.sub.on to V.sub.off at time t.sub.2, the MOS transistor is again brought to the "on" state so that the SI thyristor unit is brought to the blocking state. However, there have been no proposals regarding a specific construction for integrating the MOS transistor, the capacitor and the SI thyristor unit illustrated in FIG. 2a, on the same chip.
Basically, the SI thyristor, which controls forward-direction current of a p.sup.+ n.sup.- n.sup.+ or p.sup.+ nin.sup.+ diode by a control electrode, is particularly superior in operating speed, as compared with a conventional thyristor which has a p.sup.+ npn.sup.+ four-layer construction. It has already been pointed out that, since conduction and interruption of the current through the SI thyristor are executed by controlling the potential barrier which occurs in the channel, a control electrode of the SI thyristor is not limited to a junction gate type, but may be a insulated gate type. This has been proposed in Japanese Patent Publication No. SHO 62-20714, Japanese Patent Publication No. SHO 62-21275, Japanese Patent Publication No. SHO 62-21276, Japanese Patent Publication No. SHO 61-48790 and the like. An example of the proposed insulated gate SI thyristor has a cross-sectional construction which is illustrated in FIG. 3. In FIG. 3, an n.sup.+ region or area 23 denotes a cathode area; a p.sup.+ area 21, an anode area; and the reference numeral 26, an insulating film. A side wall section of each of cut-into recesses has a thin portion which is brought to a gate insulating film. Positive voltage is applied to a gate electrode 25, whereby the gate insulating film forms a channel just below the gate insulating film, to remove the potential barrier on the front surface of the cathode, thereby turning on the insulated gate SI thyristor. A cathode electrode 23' is in ohmic contact with both of an n.sup.+ area 23 and a p.sup.+ area 24. Many of holes flowing from the anode flow into the p.sup.+ area 24. Turning-off of the insulated-gate SI thyristor is realized by application of negative voltage to the gate electrode 25. The p.sup.+ area 24 could be formed in not common to the cathode area, but an independent electrode could be formed. In this case the holes could be drawn from the p.sup.+ area 24 at turning-off and the insulated gate SI thyristor could be turned off at a further high speed. However, a gate drive circuit is complicated. In any case, a specific structure in which the MOS transistor is connected to the location between the gate and the cathode and the gate capacitor is connected to the gate p.sup.+ region and they are integrated on the same chip of the SI thyristor unit has not at all been disclosed in the insulated gate SI thyristor which has already been proposed.